Many renewable energy technologies, while economically viable and environmentally beneficial, suffer from the disadvantage of periodic and unpredictable power generation. To enable such renewable energy technologies to expand, large scale energy storage systems are required. Additionally, many conventional electric generation technologies, such as coal and nuclear power plants, as well as promising alternative energy generation technologies, such as fuel cells, function best when operated at constant power, and thus can benefit from energy storage systems that can deliver peak power when needed and store energy during off-peak hours.